In early-stage research where the total number of cells required from a cell culture run are relatively small, adherent-based cells may be grown on cell culture vessels with flat surfaces such as T-flasks or roller bottles that have been surface-treated with substrates required for cell attachment. However, scaling up to larger volumes in these flat culture vessels quickly becomes impractical from the standpoint of vessel footprint, processing time, and media costs.
Micro-carriers are small (typically 100-200 micron in diameter), surface-treated spheres that serve as scaffolds for anchorage-dependent cells to attach and grow on while being suspended in bioreactor systems. They are ideal for scaling up anchorage-dependent cells, as they greatly increase the surface area for cells to grow on by utilizing the entire volume of the bioreactor instead of just the outer surfaces of the vessels, as in flat culture vessels. Prior to use in a bioreactor, micro-carriers are typically hydrated in phosphate buffered saline solution and then heat-sterilized in bottles in an autoclave prior to transfer into a bioreactor via an aseptic connection.
Single-use bioreactors consist of disposable vessels that have been pre-sterilized by the manufacturer, typically by gamma radiation, to eliminate the cleaning requirements by the end user. Micro-carriers that can withstand gamma radiation at sterilization dosage may be pre-loaded inside the disposable bioreactor vessel assembly by the manufacturer for sterilization by gamma radiation prior to shipping. The end user would then simply add medium aseptically and allow the micro-carriers to hydrate while being mixed prior to inoculation with cells.